大跨度钢桁拱桥关键节点受力特性及优化研究

Study on Stress Properties and Optimization of Critical Nodes of Long-span Steel Truss Arch Bridge

钢桁拱桥是以承压为主的结构体系,随着跨径的不断增大,其非线性效应会变得十分突出,因此选取关键节点进行受力状态分析就显得尤为重要。选取国内具有代表性的公路钢桁架拱桥(100 m+400 m+100 m=600 m)关键节点作为研究对象。该桥下拱肋与下弦杆交汇处的节点(B9节点)采用焊接整体节点,节点板将主桁相关杆件和桥面纵、横梁连成一体,各构件内部加劲肋众多,形式、尺寸多样,节点的结构构造和受力状态复杂。在全桥空间有限元分析的基础上,选取具有代表性的B9节点和两个最不利的主力组合工况,完成了局部精细有限元分析。结果表明:两个工况下B9节点各相关杆件绝大部分区域应力水平较低,Mises等效应力小于200 MPa,局部区域应力集中程度较严重,应力水平超出了弹性范围。针对拱内下弦杆变截面处出现的高应力区域的情况提出了改善措施,提出在该位置增设一道环形横隔板,该方案可不影响下弦杆内的柔性系杆通过。增设横隔板后,变截面处的应力集中现象得到明显改善,应力水平在弹性范围以内。

The steel truss arch bridge is the structural system dominated by the pressure.With the continuous increment of span,its nonlinear effect will become very prominent.Therefore,it is particularly important to select the critical nodes for the analysis of stress state.The critical nodes of the representative highway steel truss arch bridge 100 m+400 m+100 m=600 m are selected as the study object.The node(B9) at the junction of lower arch rib and lower boom of this bridge is used of the welded integral node.The node plate will connect the relevant rod pieces of the main truss with the longitudinal and horizontal beams of bridge deck.The stiffening rib within each component is numerous,the forms and sizes are various,and the structural construction and the stress state of nodes are complex.On the basis of the whole bridge space finite element analysis,the selection of the representative node B9 and two worst main combination conditions completes the local fine finite element analysis.The result shows that the most of regional stress level of each relevant rod piece at the node B9 under two working conditions are lower,the Mises equivalent stress is lower than 200 MPa,the local regional stress concentration degree is more serious,and the stress level exceeds the elastic range.Aiming at the high stress region appearing at the variable cross section of lower boom in the arch,the improvement measures of adding a ring diaphragm plate at this position are proposed.This scheme will not influence the flexible bowstring passing through the lower boom.After the diaphragm plate is added,the stress concentration appearance at the variable cross section is obviously improved,and the stress level is within the elastic range.